1. Field of the Invention
The present invention relates to a remote center compliance device, and more particularly, to a remote center compliance device having a measuring sensor provided at a limiter, a measuring block, or an elastic body to measure a correction amount of a force-insertion or location error of a force-insertion apparatus.
2. Description of the Related Art
Generally, in mass-producing various machinery parts (e.g., transmission, engine, steering system, motor, gearbox, etc.), precise parts such as bearing, oil seal, bush, precise shaft, and pin are automatically inserted into bearing bore, housing, shaft hole, and pin hole by using robots or dedicated assembly apparatus.
FIG. 1 is a cross-sectional view of a conventional force-insertion apparatus. Referring to FIG. 1, a boss support 2 is provided on a frame 1, and a boss B is fixed to the boss support 2. A lifter 3 is provided above the boss support 2, and a part A to be force-inserted into the boss B is fixed to the lifter 3. The lifter 3 lifts to insert the part A into the boss B forcibly. A guide 4 supports the lifting of the lifter 3. A hydraulic system 5 generates a lifting force to lift the lifter 3 along the guide 4.
A hydraulic force generated from a hydraulic pump of the hydraulic system 5 is provided to a hydraulic cylinder and the hydraulic cylinder moves up or down. The lifter 3 fixed to the hydraulic cylinder moves up or down along a lifting direction of the hydraulic cylinder. The lifter 3 has a vertical lifting force due to the guide 4, and the part A fixed to the lifter 3 is force-inserted into the boss B fixed to the boss support 2.
In addition, the boss B into which the part A is force-inserted is extracted from the boss support 2 by a separate extracting device. After a new boss B is placed, the lifter 3 rises and a new part A is fixed. In this way, the force insertions are successively performed.
The boss B refers to parts having a space such as housing, pulley, shaft hole, and pin hole. The force-insertion part A refers to parts to be force-inserted into a space such as bearing, oil seal, bushing, pin, and shaft.
However, a conventional force-insertion apparatus performs only a force-insertion work to forcibly insert the force-insertion part into the boss using a hydraulic pressure. Therefore, when the centers of the boss and the force-insertion part are not matched with each other, the force insertion causes the boss or the force-insertion part to be damaged, or the force-insertion apparatus is damaged.
One of approaches to solving these problems is disclosed in Korean Patent Laid-open Publication No. 2001-85013, filed by the present applicant and entitled “REMOTE CENTER COMPLIANCE DEVICE FOR FORCED INSERTION”. According to this application, the remote center compliance device includes an upper structure, a lower structure, and a plurality of elastic bodies between the upper structure and the lower structure, and a limiter. The remote center compliance device uses the principle of elastic center. The principle of elastic center is a mechanical principle that when an elastic is located near an object belonging to the remote center compliance device and an external force acting on the object passes through the elastic center, only a translation is performed in a direction of the external force without performing a rotation and, when a moment acts on the elastic center, the object performs only a rotation centering on the elastic center without performing a translation.
Therefore, when the remote center compliance device proposed by the present applicant is attached to the conventional force-insertion apparatus, that is, the remote center compliance device is fixed to the lifter 3, the boss B and the force-insertion part A are arranged centering on the central axis by the translation of the elastic body and are mutually force-inserted.
However, the force-insertion apparatus with the remote center compliance device or the conventional force-insertion apparatus has no unit that can measure a force-insertion force of the boss and the force-insertion part. Therefore, the force-insertion force of the part force-inserted into the boss cannot be measured.
The purpose of measuring the force-insertion force of the boss and the force-insertion part is to determine the force-insertion quality and lifetime of the boss and the force-insertion part according to how much the force-insertion part is inserted into the boss by the force-insertion force. If the force-insertion force of the boss and the part does not reach an allowable error, the part is easily released from the boss. If the force-insertion force exceeds the allowable error, the boss and the part are damaged by an excessive force insertion.
FIG. 2 is a cross-sectional view of a force-insertion apparatus including a conventional remote center compliance device and a load cell. Referring to FIG. 2, the force-insertion apparatus including the remote center compliance device of the present applicant and the load cell can correct the center error and measure the force-insertion force. In the force-insertion apparatus, the remote center compliance device 10 is provided under the lifter 3, and the load cell 20 is provided above the lifter 3.
FIG. 3 is an enlarged view illustrating the assembly of the remote center compliance device and the load cell of FIG. 2. Referring to FIG. 3, the load cell 20 is provided inside a lift platform of the lifter 3 lifting along a guide rail of the guide 4. A cover 22 transfers a weight to the load cell 20. In the remote center compliance device 10, a tool for replacing and fixing the force-insertion part A is provided under the cover 22. A bracket 12 fixes the cover to the lift platform.
However, the force-insertion apparatus including the remote center compliance device and the load cell has problems in that as the number of parts increases, the price of the products rises, a manufacturing process and structure are so complicated that the maintenance cost increases, and a wider installation space is occupied, thus lowering the product competitiveness.
In addition, a guide member called an LM guide is widely used as the guide 4. However, the LM guide is so expensive that the design and manufacturing cost of the apparatus using the LM guide will increase.
In the conventional force-insertion apparatus of FIG. 1, when the load cell 20 is mounted on the lifter 3 but the remote center compliance device 10 is not used, the force-insertion force acting between the part A and the boss B cannot be correctly measured because of the location error of the central axes.
Especially, in case where the remote center compliance device 10 is not mounted and the boss B and the part A have the center error, if the force insertion is performed in such a state that a lower portion of the initial force-insertion part A is in contact with an upper portion of the boss B, the force-insertion force measured in the load cell 20 is a sum of a force-insertion force of the lifter, a deforming force of the boss B and the part A due to the center error, and an unnecessary frictional force of the hydraulic cylinder and the guide.
On the other hand, as illustrated in FIGS. 2 and 3, when the remote center compliance device 10 corrects the center error of the part A and the boss B and force-inserts them, the actual force-insertion force alone is measured in the load cell 20. Therefore, compared with the force-insertion apparatus of FIG. 1, the force-insertion force is more correctly measured. However, as the number of parts increases, the price of the products increase, the manufacturing process and structure are so complicated that the maintenance cost increases, and a wider installation space is occupied, thus lowering the product competitiveness.